1. Field of the Invention
The present invention relates to a photovoltaic module, and is particularly suitable for a photovoltaic module which receives light on both sides.
2. Description of the Related Art
Photovoltaic power generation which converts light energy into electric energy by utilizing the photoelectric conversion effect is widely used as a means to obtain clean energy, which contributes to the global environment. In line with the improvement of solar cells' photoelectric conversion efficiency, many photovoltaic power generation systems using photovoltaic modules are installed for residential use.
In a photovoltaic module provided with a solar cell which generates electricity utilizing sunlight, conductive materials to form a positive electrode and a negative electrode are disposed in the photovoltaic module in order to output electricity generated by the solar cell to the outside. Edges of the conductive materials are taken out of the photovoltaic module as connecting terminals to which a cable for outputting electric current to the outside is connected, thereby extracting electric current.
The connecting terminals are provided by protruding the conductive materials from an edge of the photovoltaic module, or by exposing the conductive materials by way of a through-hole formed on a cover material of the photovoltaic module.
Connecting parts between the connecting terminals and the cable are stored in a housing called a terminal box for the purpose of protecting the connecting parts or preventing leakage of electricity. Usually, the terminal box is attached in the final process because the terminal box is obstructive during the production process. The terminal box is fixed by an adhesive or is screwed to an outer frame at the opposite side of a light-receiving surface of the photovoltaic module in order to reduce the weight load on the conductive materials, connecting terminals or connecting parts, and to avoid looseness in them by vibration or metal fatigue.
FIG. 27 and FIG. 28 are a cross-sectional view and a plan view respectively of a relevant part of a conventional photovoltaic module. As illustrated in FIG. 27 and FIG. 28, the photovoltaic module 1000 comprises a board-shaped photovoltaic submodule (photovoltaic panel) 50 including a plurality of solar cells 51 and an outer frame 60 made of aluminum for example set around the outer circumference of the photovoltaic submodule 50 through the intermediary of a sealing material 56. The photovoltaic submodule 50 has a plurality of solar cells 51 interposed between a light-receiving (front surface) side light-transmitting insulative substrate 52 made of low iron tempered glass for example and a rear surface side weatherproof substrate 53. A sealing resin 54 such as ethylene vinyl acetate (EVA) fills the inner gap.
The outer frame 60 is made by extruding aluminum. A fitting part 62 which is channel-shaped in a cross section and which pinches the photovoltaic submodule 50 is included in the upper part of a main body 61. The main body 61 is hollow inside to save the weight as well as relatively thick-walled and robust. A terminal box 70 is adhered and fixed to the rear surface side substrate 53, with one end of the terminal box 70 abutting on the inner side of the outer frame 60. If needed, the terminal box 70 is screwed to the outer frame 60.
Attachment of the terminal box 70 is not problematic to a photovoltaic module which receives light on one side, because the terminal box sits at the back of the solar cell, thereby not preventing receipt of light.
When the terminal box is used for a photovoltaic module which receives light on both sides, however, the terminal box reduces power generated by elements in parts of the solar cells 51 covered with the terminal box as illustrated in FIG. 27. This is because a large part of the terminal box is protruding to the power generation part. In order not to cover the solar cell with the terminal box 70, ineffective parts which do not contribute to power generation need to be increased by enlarging the substrates 52 and 53, which also enlarges the photovoltaic module.
Additionally, a connecting tub 55 connected to the terminal box 70 for extracting electricity is subject to damage because it is interposed between the substrate 53 and the outer frame 60. The connecting tub 55 has an insulating coating on its surface since it contacts the outer frame 60 made of metal. Damage to the insulating coating of the connecting tub 55 could lead to an insulation failure. The insulating coating thus needs to be thick to prevent an insulation failure in case of damage, which increases the manufacturing cost of the connecting tub 55.
A photovoltaic module which receives light on both sides is suggested in which the degree of freedom in formation of the photovoltaic module is high because at the time the terminal box is attached, the front and the back of the photovoltaic module are not identified (e.g. Japanese unexamined patent publication No. 2003-158285). The publication discloses a method for manufacturing a photovoltaic module in which a plurality of solar cells which receive light on both sides are disposed between a plurality of light-transmitting cover materials, an electrode terminal for outputting generated current is protruding from an edge between the plurality of the light-transmitting cover materials, and a terminal box housing a connecting part between the electrode terminal and a cable for outputting generated current to the outside is provided at the edge. The terminal box is attached so that its outward form is in parallel with the front and the rear surfaces of the photovoltaic module, and is nearly symmetric with respect to a center face located in the center. The attached terminal box is housed in a hollow of a frame to form the photovoltaic module.